Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Equity investments in unconsolidated subsidiaries	$ 145		$ 145		$ 141
Revenues	2,577	$ 2,658	5,718	$ 5,609
Net income	238	265	553	556
Regulated Electric
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues	2,250	2,348	4,575	4,618
Net income	249	264	482	483
Regulated Natural Gas
Segment Reporting Information [Line Items]
Equity investments in unconsolidated subsidiaries	145		145		$ 141
Revenues Including Intersegment Revenues			1,103	955
Net income	23	27	128	121
All Other
Segment Reporting Information [Line Items]
Net income	(34)	(26)	(57)	(48)
Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	2,249	2,348	4,574	4,617
Regulated Operating Revenue, Gas	308	292	1,102	954
Regulated Operating Revenue, Other	20	18	42	38
Regulated Operating Revenue	2,578	2,658	5,720	5,611
Revenues	2,577	2,658	5,718	5,609
Total revenues | Regulated Electric
Segment Reporting Information [Line Items]
Revenues	2,249	2,348	4,574	4,617
Total revenues | Regulated Natural Gas
Segment Reporting Information [Line Items]
Revenues	308	292	1,102	954
Total revenues | All Other
Segment Reporting Information [Line Items]
Revenues	20	18	42	38
Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	1	0	1	1
Regulated Operating Revenue, Gas			1	1
Regulated Operating Revenue	$ (1)	$ 0	$ (2)	$ (2)